OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 1 2025 Fig. 3. SEM/EDS analysis on the Al-Si alloy-matrix; (a), (c) microstructure; (b), (d) EDS of α-Al dendrites and inter-dendritic regions in (a), (c), respectively a b c d Fig. 4. The microstructure of the casting solidified in 29 mm wall thickness steel mold at: (a) distance of 9 mm from mold wall surface; (b) distance of 4 mm from mold wall surface a b et al. [31] investigated the influence of cooling rate on the mechanical properties and microstructure of Al-7Si alloys. According to their findings, a greater undercooling caused by a higher cooling rate, which promotes a reduction in the critical nucleus radius. As a result, the nucleation process is facilitated. However, under high cooling rate conditions, the fine grains do not have sufficient time to grow. Increasing the cooling rate promotes the formation of a finer microstructure. Nucleation occurs more readily with slight undercooling. During surface solidification, numerous nuclei form and grow ahead of the solidification front. An increase in the number of nucleation sites leads to the formation of a finer structure with a larger number of grains. During the solidification of a medium-sized casting, the solidification front moves from the surface to the center. This results in the formation of a homogeneous fine-grained structure throughout the cross-section.
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